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rcu: Fix accelerated grace periods for last non-dynticked CPU 

It is invalid to invoke __rcu_process_callbacks() with irqs
disabled, so do it indirectly via raise_softirq().  This
requires a state-machine implementation to cycle through the
grace-period machinery the required number of times.

Located-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <1267231138-27856-1-git-send-email-paulmck@linux.vnet.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Paul E. McKenney 2010-02-26 16:38:56 -08:00 committed by Ingo Molnar
parent f5f6540964
commit a47cd880b5
3 changed files with 57 additions and 20 deletions
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3
kernel/rcutree.c
View File

@ -1341,6 +1341,9 @@ static void rcu_process_callbacks(struct softirq_action *unused)
* grace-period manipulations above.
*/
smp_mb(); /* See above block comment. */
/* If we are last CPU on way to dyntick-idle mode, accelerate it. */
rcu_needs_cpu_flush();
}
static void

1
kernel/rcutree.h
View File

@ -373,5 +373,6 @@ static int rcu_preempt_needs_cpu(int cpu);
static void __cpuinit rcu_preempt_init_percpu_data(int cpu);
static void rcu_preempt_send_cbs_to_orphanage(void);
static void __init __rcu_init_preempt(void);
static void rcu_needs_cpu_flush(void);
#endif /* #ifndef RCU_TREE_NONCORE */

59
kernel/rcutree_plugin.h
View File

@ -973,9 +973,19 @@ int rcu_needs_cpu(int cpu)
return rcu_needs_cpu_quick_check(cpu);
}
/*
* Check to see if we need to continue a callback-flush operations to
* allow the last CPU to enter dyntick-idle mode. But fast dyntick-idle
* entry is not configured, so we never do need to.
*/
static void rcu_needs_cpu_flush(void)
{
}
#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
#define RCU_NEEDS_CPU_FLUSHES 5
static DEFINE_PER_CPU(int, rcu_dyntick_drain);
/*
* Check to see if any future RCU-related work will need to be done
@ -988,39 +998,62 @@ int rcu_needs_cpu(int cpu)
* only if all other CPUs are already in dynticks-idle mode. This will
* allow the CPU cores to be powered down immediately, as opposed to after
* waiting many milliseconds for grace periods to elapse.
*
* Because it is not legal to invoke rcu_process_callbacks() with irqs
* disabled, we do one pass of force_quiescent_state(), then do a
* raise_softirq() to cause rcu_process_callbacks() to be invoked later.
* The per-cpu rcu_dyntick_drain variable controls the sequencing.
*/
int rcu_needs_cpu(int cpu)
{
int c = 1;
int i;
int c = 0;
int thatcpu;
/* Don't bother unless we are the last non-dyntick-idle CPU. */
for_each_cpu_not(thatcpu, nohz_cpu_mask)
if (thatcpu != cpu)
if (thatcpu != cpu) {
per_cpu(rcu_dyntick_drain, cpu) = 0;
return rcu_needs_cpu_quick_check(cpu);
}
/* Try to push remaining RCU-sched and RCU-bh callbacks through. */
for (i = 0; i < RCU_NEEDS_CPU_FLUSHES && c; i++) {
c = 0;
/* Check and update the rcu_dyntick_drain sequencing. */
if (per_cpu(rcu_dyntick_drain, cpu) <= 0) {
/* First time through, initialize the counter. */
per_cpu(rcu_dyntick_drain, cpu) = RCU_NEEDS_CPU_FLUSHES;
} else if (--per_cpu(rcu_dyntick_drain, cpu) <= 0) {
/* We have hit the limit, so time to give up. */
return rcu_needs_cpu_quick_check(cpu);
}
/* Do one step pushing remaining RCU callbacks through. */
if (per_cpu(rcu_sched_data, cpu).nxtlist) {
rcu_sched_qs(cpu);
force_quiescent_state(&rcu_sched_state, 0);
__rcu_process_callbacks(&rcu_sched_state,
&per_cpu(rcu_sched_data, cpu));
c = !!per_cpu(rcu_sched_data, cpu).nxtlist;
c = c || per_cpu(rcu_sched_data, cpu).nxtlist;
}
if (per_cpu(rcu_bh_data, cpu).nxtlist) {
rcu_bh_qs(cpu);
force_quiescent_state(&rcu_bh_state, 0);
__rcu_process_callbacks(&rcu_bh_state,
&per_cpu(rcu_bh_data, cpu));
c = !!per_cpu(rcu_bh_data, cpu).nxtlist;
}
c = c || per_cpu(rcu_bh_data, cpu).nxtlist;
}
/* If RCU callbacks are still pending, RCU still needs this CPU. */
if (c)
raise_softirq(RCU_SOFTIRQ);
return c;
}
/*
* Check to see if we need to continue a callback-flush operations to
* allow the last CPU to enter dyntick-idle mode.
*/
static void rcu_needs_cpu_flush(void)
{
int cpu = smp_processor_id();
if (per_cpu(rcu_dyntick_drain, cpu) <= 0)
return;
(void)rcu_needs_cpu(cpu);
}
#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */